The invention relates to a method for automatically determining the position of transceivers of navigation signals.
Satellite systems for global navigation (GNSS; GNSS=global navigation satellite system) are used for position finding and navigation on the ground and in the air. GNSS systems, such as the European satellite navigation system that is currently under construction (hereinafter also referred to as the Galileo system or simply Galileo), comprise a plurality of satellites or pseudolites, an earth-based receiver system, which is connected to a central calculating station, and utilization systems, which evaluate and use the navigation signals, transmitted from the satellites or pseudolites.
In general it is necessary to know in a navigation environment, in particular a GNSS, the exact position of the transmitters, which are beaming the navigation signals for reception by the utilization systems, in a coordinate system. In a satellite navigation system it is very important to know the Kepler parameters for the orbits of satellites for an exact navigation. Usually the exact positions of terrestrial GNSS—that is, pseudolite systems—are determined using a complicated calibration of the transmitters of the navigation signals. Initial attempts have already been made to determine the positions of the navigation transmitters by means of a self-calibration.
The following publications describe the self-calibration of transmitters of navigation signals:                “Self-Calibration of Pseudolite Arrays Using Self-Differencing Transceivers”, E. A. LeMaster, S. M. Rock, Proceedings of the Institute of Navigation GPS-99 Conference, Nashville, Tenn., September 1999, pp. 1549-1558;        “Field Test Results for a Self-Calibrating Pseudolite Array”, E. A. LeMaster, S. M. Rock, Proceedings of the Institute of Navigation GPS 2000 Conference, Salt Lake City, September 2000, pp. 1046-1055;        “An Improved Solution Algorithm for Self-Calibrating Pseudolite Arrays”, E. A. LeMaster, S. M. Rock, Institute for Navigation National Technical Meeting, San Diego, Calif., January 2002;        “Field Demonstration of a Mars Navigation System Utilizing GPS Pseudolite Transceivers”, E. A. LeMaster, S. M. Rock, Position, Location, and Navigation Symposium, Palm Springs, Calif., April 2002; and        “3-D Capabilities for GPS Transceiver Arrays”, M. Matsuoka, E. A. LeMaster, S. M. Rock, Proceedings of the Institute of Navigation GPS 2002 Conference, Portland, Oreg., September 2002, pp. 824-834.        
The major drawback with the methods and the systems described in these publications is that a utilization system has to be designed as a transceiver and, thus, has to be also able to transmit, a feature that is not always desired, especially in the case of military applications. If there are a number of users in the navigation system, then it is advantageous with respect to a limited bandwidth if the individual users do not have to transmit any navigation signals. Another drawback with the design of the utilization system as the transceiver is that complex, weight and cost-intensive hardware is required for the utilization system.
Therefore, exemplary embodiments of the present invention provide a method and a device for automatically determining the position of transceivers of navigation signals. In this case a utilization system for self-calibration does not have to be designed as the transceiver.
Exemplary embodiments of the invention involve applying a multi-step self-calibrating algorithm for transceivers of navigation signals using a utilization system for determining the position of the transceivers. According to such an algorithm, the self-calibration of a network of transceivers is carried out in three steps:                1. coarse calibration of the coordinates of the transceivers;        2. estimate of the trajectory of the utilization system; and        3. fine calibration of the coordinates of the transceivers and the trajectory of the utilization system on the basis of the coarse calibration and the estimate of the trajectory.        
The self-calibration of the transceiver coordinates significantly reduces the amount of time required to set up a local navigation environment, for example, for a temporary landing field or for indoor navigation in certain buildings. Furthermore, it is not necessary to design a utilization system as a navigation transmitter, a feature that is very important for military applications in order to avoid detection by an enemy. The application of passive utilization systems makes it possible, in light of limited bandwidths, that the number of users in the navigation environment does not have to be restricted. Finally the invention allows the use of lightweight and inexpensive user hardware.
According to one aspect of the present invention, a method for automatically determining the position of transceivers of navigation signals with the use of a utilization system for the navigation signals and has the following steps:                a) coarse calibration of the coordinates of the transceivers;        b) estimate of the trajectory of the utilization system; and        c) fine calibration of the coordinates of the transceivers and the trajectory of the utilization system on the basis of the coarse calibration and the estimate of the trajectory.        
In another aspect of the invention, the distance between two transceivers is determined using the coarse calibration.
According to an additional aspect of the invention, self-differenced observation equations can be used for the coarse calibration. This procedure makes possible the direct observation of the distance between two transceivers.
Furthermore, according to one aspect of the invention, the method can be designed in such a manner that, after the distance between all transceivers has been determined, a rough estimate of the coordinates of the transceivers can be made by triangulation of the determined distance between the transceivers. In this way the transceivers can be arranged in a local coordinate system.
An additional aspect of the invention provides that a local coordinate system is used, in order to determine the coordinates of the transceivers, and the optimal position of the coordinate system with respect to the transceivers is automatically sought. The introduction of a local coordinate system makes it possible to restrict the system because within a network of transceivers only positioning in relation to each other is possible. Furthermore, owing to the automatic search for the optimal position of the coordinate system, it is possible to improve the success rate of the self-calibration even in the case of difficult geometries and extremely noisy measurements.
In another aspect of the invention, the starting position of the utilization system is determined after step a), but before step b) is carried out.
For a first estimate of the starting position of the utilization system, one aspect of the invention provides that double differenced pseudoranges can be used as the observation variable. In this way the clock errors of the transceivers and the navigation system are compensated, if the transmitters for the navigation signals in the transceivers are not synchronized.
Furthermore, in one aspect of the invention, the starting position of a utilization system can be determined by a grid network search, based on a minimization of measurement residuals.
In another aspect of the invention, the sum of squared measurement residuals is determined for each grid network point and used as the test variable, in order to differentiate between the different test candidates of the grid network points for the starting position.
According to one aspect of the invention, that grid network point that yields the minimum sum of squared measurement residuals can be selected as the first estimate of the starting position.
According to another aspect of the invention, the grid network search is carried out in the first step with a coarse grid network, which covers the total area of the navigation environment, and in the subsequent step with a fine grid network, which is spanned around the grid network point, selected in the previous step.
According to an additional aspect of the invention, the dimensions of the test area for determining the starting position of the utilization system are determined by means of the coarse-calibrated coordinates of the transceivers.
According to another aspect of the invention, the trajectory of the utilization system can be estimated using an iterative least square approach while simultaneously exploiting the small dynamics of the utilization system in a linearization of the observation equations.
According to one aspect of the invention, only low noise phase measurements of the navigation signals, transmitted by the transceivers, are used for the fine calibration of the coordinates of the transceivers and the trajectory of the utilization system.
In an additional aspect of the invention, the fine calibration of the coordinates of the transceivers and the trajectory of the utilization system is carried out using an iterative least square approach.
For the iterative least square approach, a Taylor series development of the observation equations is carried out, according to one aspect of the invention. Either this Taylor series development is terminated after the linear term, and then a standard iterative least square method is employed for the fine calibration, or the Taylor series development is terminated after the quadratic term, and then a quadratic iterative least square method is employed.
In another aspect of the invention, double differenced observation equations are used for the fine calibration.
Finally, in one aspect of the invention, so many iterations are carried out in the framework of the iterative least square approach until either the convergence criterion or the divergence criterion is fulfilled, or the maximum allowable number of iterations is exceeded.
Furthermore, one aspect of the invention provides that the fine calibration is repeated with the use of the results that vary from the results of the coarse calibration.
In addition, in one aspect the invention relates to a computer program for carrying out the method of the invention.
An additional aspect of the invention provides a computer program product, which comprises a machine readable program carrier, on which a computer program is stored, according to the invention, in the form of electronically and/or optically readable control signals.
Furthermore, the invention relates, according to one aspect, to a device for automatically determining the position of the transceivers of navigation signals with the use of a utilization system for the navigation signals. In this case the device comprises:                a first means for coarse calibration of the coordinates of the transceivers;        a second means for estimating the trajectory of the utilization system; and        a third means for the fine calibration of the coordinates of the transceivers and the trajectory of the utilization system.        
Furthermore, one aspect of the invention provides four means for determining the starting position of the utilization system.
The first to fourth means can be implemented, in particular, by means of a processor and a memory, in which is stored a program of the invention for execution by the processor.
Other advantages and possible applications of the present invention are disclosed in the following description in conjunction with the embodiments depicted in the drawings.